This invention relates to providing a system for improved exhaust evacuation from an internal combustion engine.
Internal combustion engines serve to power a majority of the powered vehicles worldwide. Typically, internal-combustion-driven vehicles comprise at least one system for transporting the exhaust gases from the combustion cylinder to at least one remote discharge point adjacent the vehicle. Commonly, the exhaust system will comprise a length of metallic pipe or similar fluid-transporting conduit. In most vehicles, the exhaust system will further include at least one sound-modifying device such as a muffler or silencer.
Typical “performance” mufflers, such as found on an off-road or road-going motorcycle, are mounted high and rearward on the vehicle. Preferably, a muffler should be located as close as possible to the center of vehicle mass (forward and downward). This preferred position improves vehicle handling by lessening the dynamic loads imposed on suspension systems by reducing the outer rotating mass of the vehicle.
In general, clearance for a muffler changes from front to rear based on a vehicle's amalgamation of fixed structures. On a motorcycle, the available room at the front of the muffler is dictated by the clearance between the rear tire, rear shock, sub-frame, brake components, and inside clearance beneath the side panels or number plate. Tire contact with a muffler will cause the muffler to move, thus weakening and eventually breaking the muffler mounts. Any contact with the vehicle frame, sub-frame, or shock will eventually cause a hole to develop at the point of wear. The side panels of most motorcycles are generally made from plastic; any contact with the muffler results in heat damage. Preferably, a muffler needs to have enough sound-absorbing media to attenuate combustion noise but not so little that the sound-absorbing media would need to be serviced too frequently. On a street or road bike, the clearance needs to be such as to allow for maximum lean angle while not making contact with the road surface causing damage to the muffler and loss of stability. A need exists for an improved muffler design that both increases the clearances between the vehicle, the muffler and the driving surface, and lessens dynamic loads imposed on suspension systems by reducing the outer rotating mass of the vehicle.
It is generally known that the performance of an internal combustion engine is affected by the fluid flow characteristics of the exhaust system. Generally, the less restrictive the system is to the passage of the exhaust gasses, the greater the performance of the engine.
Internal combustion engines operate by drawing power from a controlled explosion within a combustion cylinder. In a typical four-stroke combustion cycle, an intake mixture of air and fuel is drawn into the combustion cylinder, compressed, ignited to produce power, and finally discharged from the engine to the exhaust system. Generally, the amount of performance derived from the engine is directly related to the volume of air/fuel mixture that can be introduced into the combustion cylinder during each cycle. Restrictions in the exhaust system can prevent full evacuation of the combustion gases from the cylinder, resulting in an inability of the engine to fully recharge the cylinder with a subsequent volume of fuel/air mixture. Therefore, deriving maximum power from any engine requires an exhaust system designed with the free-flow of exhaust gases as a primary objective. Unfortunately, exhaust systems often sacrifice flow in favor of other factors, for example, the reduction of sound emissions during operation.
Those who operate high performance vehicles are especially concerned with exhaust performance. Traditional methods of increasing performance of engines include increasing cylinder compression, valve modifications, and aggressive cam profiles. Each method has distinct disadvantages from the standpoint of heat generation, reliability, and engine longevity. Alternately, increasing the performance of the exhaust system may increase engine power output with relatively minor reductions in reliability.
A common practice used to meet closed course sound regulations in competitive motorcycle racing, is to use a very small diameter muffler core and an even smaller diameter outlet. The negative consequences of this arrangements is that low and mid RPM torque diminishes when compared to the performance characteristics of a large core, large outlet system.
A need exists for an exhaust system to overcome this problem while fully complying with the requirements of the American Motorcyclist Association (AMA) and Federation Internationale de Motorcyclisme (FIM) closed course sound regulations.
Furthermore, due to increasing pressure from controlling bodies to set decibel sound limits for motorized vehicles operating within public lands, a need exists for a high-performance exhaust system that provides necessary reductions in sound emissions, while maintaining a high degree of performance.